omit debian directory in source build

While this is not a problem when building the source release from this repo, it is an issue when building from the debian packaging repo, as the debian folder should not be part of the upstream source release.

However, the packaging repo run the same tar command and it will have all the upstream source + the debian/ folder, which is a problem because the next CI jobs will use the output of the source release job to build a .deb file.